The invention concerns a multi-circuit protection valve for a compressed-air supply device of a vehicle, in particular a truck, with a first port for a service brake, wherein the first port has two separate service brake circuit ports for a first service brake circuit and a second service brake circuit, and wherein the first service brake connection is secured by a first service brake circuit overflow valve and the second service brake circuit port is secured by a second service brake circuit overflow valve, and with a second port for a parking brake which is secured by an overflow valve, wherein the first service brake circuit or the second service brake circuit can be filled as priority, and wherein the overflow valve has a first active face which can be pressurized with a valve input pressure and a second active face which can be pressurized with a valve output pressure.
The invention furthermore concerns a method for operating a multi-circuit protection valve for a compressed-air supply device of a vehicle, in particular a truck, with a first port for a service brake, wherein the first port comprises two separate service brake circuit ports for a first service brake circuit and a second service brake circuit, and wherein the first service brake circuit port is secured by a first service brake circuit overflow valve and the second service brake circuit port is secured by a second service brake circuit overflow valve, and with a second port for a parking brake which is secured by an overflow valve, wherein the first service brake circuit or the second service brake circuit is filled as priority.
Modern vehicles, in particular trucks and heavy goods vehicles, often have a pneumatically driven brake system which is composed of a service brake and a parking brake. Normally the service brake is opened in pressureless state, while the parking brake is closed in pressureless state in order to allow secure parking of the vehicle. Consequently, to close the service brake and open the parking brake, loss-free service pressures are required in the respective function circuits. In order to be able to exert a braking force on the vehicle at any time, it is prescribed that the service brake must be filled to a sufficient pressure level for braking the vehicle before the parking brake. This ensures that the parking brake cannot be released until sufficient braking effect can be provided via the service brake.
To fulfill this legal requirement, various solutions are known in the prior art, wherein the fundamental idea in all cases is based on the supply to the parking brake circuit, i.e. the filling of this circuit, being delayed until sufficient pressure and hence braking force is present or can be provided in the service brake.
It is known, for example, to provide a parallel flow to overflow valves, which separate two mutually independent service brake circuits of the service brake, from a central region of a multi-circuit protection valve. On the output side, i.e. in the direction towards the respective service brake circuit, a branch with a non-return valve branches off downstream of the respective overflow valve. The two branches open into a common pressure line, from which in turn the parking brake circuit is supplied via an overflow valve. In this way it is ensured that at least one of the two service brake circuits has an operating pressure at the level of the opening pressure of the overflow valve securing the parking brake circuit, before this opens and the parking brake circuit is supplied with compressed air.
As a further solution it is known to fill the service brake circuit and parking brake circuit from a central region in parallel to each other, wherein overflow valves are arranged in the respective ports and can be filled in parallel with each other. The filling sequence can be achieved via different opening pressures of the overflow valves, wherein sufficiently great safety intervals must be observed between the different opening pressures in the service brake circuit and the parking brake circuit.
It is also known to fit a 2/2-way blocking valve which can be controlled with the service pressures from the service brake circuits in order to prevent the supply to, i.e. the filling of, the parking brake circuit. If, to open this blocking valve, a sufficient operating pressure is necessary in one or more service brake circuits, the legal requirement with regard to the filling sequence is also fulfilled.
An alternative solution, which can be used in particular if the air preparation unit has an electronic control system, is to monitor the pressure in the service brake circuits. The supply to the parking brake circuit is blocked as long as the measured pressures are not sufficient to generate the necessary braking force. To this end, suitably a 3/2-way valve, which can be designed as a solenoid valve, can conduct pressure into a spring chamber of the overflow valve securing the parking brake circuit, so that the maximum available pressure in the central region, from which the parking brake circuit is supplied, is insufficient to open the overflow valve. Only when sufficient pressure is detected in the service brake circuits is the spring chamber purged via the solenoid valve, so that the pressure in the central region is sufficient to open the overflow valve. From this moment, the parking brake circuit is supplied with compressed air.
The object of the present invention is to propose an alternative, purely pneumatic solution.
The invention is based on the prior art in that the overflow valve has a third active face which can be pressurized with a service brake pressure from the service brake circuit of the service brake which was not filled as priority, and that the forces generated via the three active faces counter a closing force to open or hold open the overflow valve. In this way the opening of the overflow valve can be made dependent on an adequate service brake pressure in both service brake circuits, since the lower service brake pressure via the third active face makes a direct contribution to the opening of the overflow valve, countering the closing force. Thus the legal requirement for the filling sequence, i.e. service brake circuit before parking brake circuit, can be fulfilled, wherein in particular both service brake circuits are filled before the parking brake circuit. Priority here can mean priority over the other service brake circuit or priority over all other consumer circuits, i.e. both over the other service brake circuit and over the parking brake circuit.
It can furthermore be provided that the first service brake circuit overflow valve has a lower opening pressure than the second service brake circuit overflow valve. In particular in this way, the first service brake circuit can always be filled first before the second service brake circuit can be filled, which again can then allow the opening of the overflow valve via the force generated on the third active face. In this way it can be ensured that the filling of both service brake circuits is completed before the parking brake circuit is filled.
It can be provided that a non-return valve is arranged parallel to the first service brake circuit overflow valve and allows a flow in the direction of the first service brake circuit port. In this way, independently of the opening pressure of the first service brake circuit overflow valve, it can be ensured that the first service brake circuit is filled as priority so that that filling of both service brake circuits is also completed before the necessary third force to open the overflow valve is generated via the service brake pressure from the second service brake circuit.
Usefully, it can be provided that the multi-circuit protection valve comprises a control valve with a first control valve inlet port, a second control valve inlet port and a control valve outlet port, wherein the two control valve inlet ports are each pressurized with one of the two service brake pressures from the two service brake circuit ports, and the control valve output port of the control valve pressurizes the third active face of the overflow valve. The control valve can, for example, be designed as a “select low” valve which outputs at the control valve output port the lower pressure present at the two control valve input ports. Thus the lower service brake pressure from the first service brake circuit or the second service brake circuit can always be used to pressurize the third active face of the overflow valve. This allows the filling of both service brake circuits before the filling of the parking brake circuit, wherein the filling sequence of the two service brake circuits can be variable, i.e. in particular also random.
Advantageously it can be proposed that the parking brake circuit is post-supplied from the service brake circuits. The post-supply can, for example, take place from the first service brake circuit, so that the valve input pressure of the overflow valve is provided from the first service brake circuit. Thus filling of at least one of the service brake circuits as priority over the parking brake circuit can be ensured.
In particular it can be proposed that the multi-circuit protection valve comprises a supply valve with a first supply valve input port, a second supply valve input port and a supply valve output port, wherein the two supply valve input ports of the supply valve are each pressurized with one of the two service brake pressures from the two service brake circuit ports, and the supply valve output port of the supply valve provides the valve input pressure of the overflow valve. The supply valve can, for example, be designed as a “select high” valve so that only one service brake circuit need be functioning in order to allow the supply of the parking brake circuit.
In can furthermore be provided that the parking brake circuit is supplied with pressure in parallel with the service brake circuits. The supply of the parking brake circuit can thus be ensured independently of a defect in the service brake circuits.
In particular it can be provided that the forces generated via the three active faces are smaller individually than the closing force. Thus the function of the overflow valve for securing the parking brake circuit can be maintained, since on an absence of the valve input pressure at the first active face and of the service brake pressure at the third active face, the force present at the second active face is not sufficient to hold the overflow valve open against the closing force. Furthermore in this way on first filling, i.e. with a pressureless parking brake circuit, it is ensured that to fill the parking brake circuit, as well as a sufficient valve input pressure at the first active face, a sufficient service brake pressure is necessary at the second active face.
It can be provided that the forces generated via the three active faces are greater in pairs than the closing force. This allows the overflow valve to be held open if a pressure drop occurs in one of the two service brake circuits.
Usefully, such a multi-circuit protection valve can be provided as part of a compressed-air supply device of a vehicle, in particular a truck.
The generic method is refined in that a first active face of the overflow valve is pressurized with a valve input pressure, a second active face of the overflow valve is pressurized with a valve output pressure, a third active face of the overflow valve is pressurized with a service brake pressure from the service brake circuit of the service brake which was not filled as priority, and forces generated via the three active faces counter a closing force to open or hold open the overflow valve.
In this way the benefits and features of the invention can also be implemented in a method.